Blue-Blooded Fire Hydrant


San Francisco fire hydrants are color-coded by where their water comes from. A water tank atop Nob Hill is the source for blue hydrants, according to Barnard Winn's "San Francisco Underfoot."
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/11/30/BAVB1AO2PJ.DTL